Processes for the treatment of a sour hydrocarbon fraction wherein the fraction is treated by contacting said fraction with an oxidation catalyst in the presence of an oxidizing agent and an alkaline component have become well-known and widely practiced in the petroleum refining industry. Said processes are typically designed to effect the oxidation of offensive mercaptans contained in a sour hydrocarbon fraction with the formation of innocuous disulfides--a process commonly referred to as sweetening. The oxidizing agent is most often air. Gasoline, including natural, straight run and cracked gasolines, is the most frequently treated sour hydrocarbon fraction. Other sour hydrocarbon fractions include the normally gaseous petroleum fractions as well as naphtha, kerosene, jet fuel, fuel oil, lube oil, and the like.
A commonly used continuous process for treating a sour hydrocarbon fraction entails treating the distillate in contact with a metal phthalocyanine catalyst dispersed in an aqueous caustic solution to yield a doctor sweet product. The sour hydrocarbon fraction and the catalyst containing aqueous caustic solution provide a liquid-liquid system wherein mercaptans are converted to disulfides at the interface of the immiscible solutions in the presence of an oxidizing agent--usually air. Sour hydrocarbon fractions containing more difficult to oxidize mercaptans are more effectively treated by contacting with a metal chelate catalyst disposed on a high surface area adsorptive support--usually a metal phthalocyanine on an activated charcoal. The sour fraction is treated by contacting with the supported metal chelate catalyst at oxidation conditions in the presence of an alkaline agent. One such process is described in U.S. Pat. No. 2,988,500. The oxidizing agent is most often air admixed with the hydrocarbon fraction to be treated, and the alkaline agent is most often an aqueous caustic solution charged continuously to the process or intermittently as required to maintain the catalyst in the caustic-wetted state.
Heretofore, the practice of catalytically treating mercaptan containing sour hydrocarbon fractions has involved the introduction of alkaline agents, usually sodium hydroxide, into the sour petroleum distillate prior to or during the treating operation. (U.S. Pat. Nos. 3,108,081 and 4,156,641). These patents along with several others which teach improvements of the basic process all deal with an oxidative method of treating mercaptans in a sour hydrocarbon fraction.
U.S. Pat. No. 3,894,107 teaches the conversion of heteroatom compounds to higher hydrocarbons over a particular type of aluminosilicate molecular sieve at temperatures of 300.degree. C.-500.degree. C., in the gas phase. Thus, if mercaptans are used in this process, the resultant products would be higher hydrocarbons and H.sub.2 S. The formation of H.sub.2 S would present a disposal problem. Therefore, because of the H.sub.2 S disposal problem and the high temperatures involved, this process is not useful as a hydrocarbon sweetening process.
The present invention discloses a non-oxidative method of sweetening a sour hydrocarbon fraction comprising contacting a mercaptan containing sour hydrocarbon fractions with an acid type catalyst in the presence of an unsaturated hydrocarbon, thereby converting said mercaptans to thioethers. The instant invention has the advantage over the oxidative method of the prior art in that no alkaline agent is involved in the present invention and therefore the problem of disposing of the spent alkaline agent is eliminated.